Power Supply And Cooling Fan Features - Dell PowerVault MD3000 Hardware Owner's Manual

Write-Back Cache
Write-back cache is a caching strategy whereby write operations result in a completion signal being sent
to the host operating system as soon as the cache receives the data to be written. The target physical disk
will receive the data at a more appropriate time in order to increase controller performance. In dual-
active controller configurations with write-back caching enabled, the write data is always copied to the
cache of the second controller before completion status is issued to the host initiator. Write Back is
enabled by default.
Write-Through Cache
Write-through cache is a caching strategy whereby data is written to the physical disk before completion
status is returned to the host operating system. Write-through cache is considered more secure than
write-back cache, since a power failure is less likely to cause loss of data. The RAID controller
automatically switches to write-through if cache mirroring is disabled or if the battery is missing or has a
fault condition. Write-through cache results in lower performance.
NOTE:
Cache mirroring and write cache settings are not user-configurable.

Power Supply and Cooling Fan Features

Your RAID enclosure supports two integrated, hot-pluggable power supply/cooling fan modules. Both
modules must be installed to ensure proper cooling. Each module contains two separate cooling fans.
The enclosure requires at least three of the cooling fans to operate to avoid overheating.
CAUTION:
A power supply/cooling fan module can be removed from a powered-on enclosure for a maximum
period of no more than 5 minutes. Beyond that time, the enclosure may automatically shut down to prevent
damage to the enclosure and/or enclosure components.
A power supply/cooling fan module can be replaced without powering down the enclosure. For
information on removing and replacing the modules, see "Removing and Installing the Power
Supply/Cooling Fan Module" on page 54.
Figure 1-7 shows the power supply/cooling fan module features and LED indicators. Table 1-5 lists the
LED indicator descriptions.
About Your System
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